LONDON (AP) -- British Olympic chiefs have clamped down on a bit of guerrilla marketing that saw the country's athletes sporting stylish - but non sponsor-brand - headphones at the games.

Many athletes use headphones to help keep focused before competitions and several have been photographed wearing the Beats by Dr. Dre brand.

The reason for their popularity? British Olympic officials say batches were shipped to hotels outside London where Team GB athletes were staying

Diver Tom Daley was seen on television wearing them before competing Monday and soccer player Jack Butland tweeted his support for the brand.

But no more. British Olympic Association spokesman Darryl Seibel said Thursday that officials have reminded team leaders of "the importance of protecting our corporate partners" and of rules against endorsing commercial products on Twitter.

He said no one had received any formal warnings or sanctions over the matter.

Olympic officials are vigilant about protecting the rights of games sponsors, which include McDonald's, Coca-Cola and electronics giant Samsung.

That has left some athletes chafing at restrictions that stop them mentioning their own sponsors. Dozens of Olympians have taken to Twitter to urge an end to the International Olympic Committee's Rule 40, which gives Olympic organizers the right to punish and even disqualify competitors if they try to pitch their own sponsors, whether on the field of play - where all advertising is barred - or online.

Seibel said British athletes are welcome to wear headphones made by games sponsor Panasonic.

The Dr. Dre brand has long been popular with musicians and athletes, and non-British Olympians including Chinese swimmer Sun Yang have been spotted wearing them.

London games organizers and the IOC said Thursday the headphone issue was a matter for national officials.